Theorem pm2.621 397

Description: Theorem *2.621 of [WhiteheadRussell] p. 107. (Contributed by NM, 3-Jan-2005.)

Assertion

Ref	Expression
pm2.621	⊢ ((φ → ψ) → ((φ ∨ ψ) → ψ))

Proof of Theorem pm2.621

Step	Hyp	Ref	Expression
1		id 19	. 2 ⊢ ((φ → ψ) → (φ → ψ))
2		idd 21	. 2 ⊢ ((φ → ψ) → (ψ → ψ))
3	1, 2	jaod 369	1 ⊢ ((φ → ψ) → ((φ ∨ ψ) → ψ))

Syntax hints:   → wi 4   ∨ wo 357

This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8

This theorem depends on definitions:  df-bi 177  df-or 359

This theorem is referenced by:  pm2.62  398  pm2.73  818  pm4.72  846  undif4  3608